Fire-retardancy of lignocellulosic materials by phosphorylating chlorinated or brominated lignocellulosics



U.S. Cl. 117-118 6 Claims ABSTRACT OF THE DISCLOSURE Improving the fire-retardant properties of lignocellulosic materials by chlorinating or brominating said materials and thereafter phosphorylating with a trialkyl or triaryl phosphite or phosphonate.

This invention relates to the flamepro fing of cellulosic compositions containing lignin and preferably to the production of lignocellulosic articles having some degree of resistance to burning. The expression lignocellulosic articles will be understood to mean lignin-containing cellulosic bodies or structures such as wooden beams, veneers or rods; paper sheets, rolls of newsprint; strawboard or chip board; yarns, webs, woven or knitted fabrics, ropes or belts made of lignocellulosic fibers such as, for example, jute, kenaf, sisal, hemp or the like. By the term products is meant to include both such articles and bulk materials.

Previous methods of rendering lignocellulosic articles ....\fiame-resistant have generally involved either the surface coating or the impregnation of the articles with inorganic salts or organic compounds having a flame retarding effect. Coating or impregnating materials which have been used for this purpose include water-soluble silicates, phosphates and borates, tin, iron, antimony and chromium oxides, and chlorinated or brominated organic compounds. It is a disadvantage of these known methods that the flame retardant composition remains as a material extraneous to the lignocellulosic article and does not bond chemically thereto. As a result in many cases, the enhanced flameresistance which is imparted to the article is gradually lost when the article is exposed to weathering or is soaked in water for any substantial length of time. In other cases relatively large amounts of the flame-retardant composi' tion are necessary which adversely affect the material thus treated.

Wood is composed of three major ingredients, namely cellulose, hemicellulose and lignin. The first two are long chain carbohydrates whilst the lignin is a compound containing condensed phenyl-propane units. Most other plant materials contain these three major ingredients although the relative amounts vary widely. Although in some cases, for example in the case of cotton, a cellulosic material manufactured from the plant is lignin-free, there are many other products in which at least some lignin is re tained. This applies in particular to ground-wood which serves as the main ingredient in the manufacture of newsprint. Such groundwood flour may contain up to about 27% of lignin depending on the species of wood from which it has been prepared and also depending on the bleaching process employed. Semi-chemical pulps serving for the production of cardboard and of corrugated sheets for the manufacture of cardboard boxes contain varying amounts of lignin. Jute and sisal fibers contain substantial amounts, as do also bast and leaf fibers.

The lignin and hemicellulose form the so-called middle lamella which occurs between the fibrous cells of wood and many other plant tissues; the lignin also occurs in the lignocellulosic fibers such as those of jute, hemp and sisal.

The middle lamella surrounds the fibrous cells, which Patented Aug. 5, 1969 This invention consists in improving the fire-retardant I properties of lignocellulosic articles in which the lignin component is halogenated.

In accordance with this invention, lignocellulosic articles having improved fire-retardant properties are obtained by 'halogenating, i.e. brominating or chlorinating the lignocellulosic material and thereafter reacting the resulting product with trialkyl or triaryl phosphites, or phosphonates wherein the alkyl groups preferably contain from 1 to 4 carbon atoms, and wherein the aryl groups may be halogenated, if desired.

Phosphites and phosphonates that are particularly useful include, for example, tgieihyhphgsghite, triphe y phosphite, tripropyl phosphite, ethyl diphenyl phosphite, tris-(2-bromoethyl) phosphite, tris-(bromopropyl) phosphite, bis-(Z-bromoethyl) 2-bromoethyl phosphonate, bis- (bromopropyl) bromopropyl phosphonate, and the like.

The temperature of reaction is from about to about 150 C. and is advantageously about to 150 C. At these temperatures the alkyl bromines undergo a Michaelis-Arbuzov reaction with the trialkyl or aryl phosphite which results in the attachment of the phosphorus to the lignin in the form of an alkyl or aryl phosphonate and the loss of an alkyl or aryl bromide. Since the aryl and secondary alkyl bromines will not undergo this reaction, they will be left to furnish the halogen necessary for the synergistic effect on the fire retardancy.

The lignocellulosic articles are advantageously halogenated to a content of from about 2 to 12 weight percent, and thereafter phosphorylated to a content of from 1 to 4 weight percent phosphorus. The extent of phosphorylation is controlled by the amount of primary alkyl bromine present, the reaction temperature and the time of reaction, which may be from a few minutes to several hours and is advantageously from about 30 minutes to about 2 hours.

The invention is further illustrated by the following examples.

Example I Five grams of hardboard fiber (groundwood) which had been brominated by the method of US. Patent 3,150,- 919 and containing 3.86 weight percent bromine by newtron activation analysis was charged to a 500 cc. flask. Triethyl phosphite, 99 g., was added and refluxed at C. for two hours.

The treated fiber was then filtered on a vacuum filter and washed twice with 2B absolute ethanol using 50 ml. each washing.

The treated, washed wood fiber was then placed in a 500 cc. flask and held at 25 C. and 1 mm. pressure for two hours to remove traces of ethanol and remaining triethyl phosphite. After removal from the flask the material was analyzed by neutron activation and found to contain 2.9 percent by weight bromine and 2.6 weight percent phosphorus. The bromine content was thus reduced to 75% of its original value.

A small amount of this treated fiber would not flame or smolder when ignited with a match flame and the flame was removed. A sample of the original brominated fiber would continue to burn.

Example II The experiment of Example I was repeated except that the phosphite employed was triphenyl phosphite (103 g.) and the temperature was C. The treated wood was analyzed by neutron activation and found to contain 3.3

percent by weight bromine and 4.36 weight percent phosphorus.

g WP THENCE SEAR-CH R'OO M A small amount of this fiber was tested with a match as in Example I and did not fiame or Smolder.

Example III In the same manner as in Example 11, 5 grams of nonbrominated hardboard fiber was treated with 102 grams of triphenyl phosphite and the unreacted phosphite was removed by washing with benzene. Analysis of this material showed 3.8 weight percent phosphorus. When placed in a match flame this material would continue to burn after removal of the flame source.

I claim:

1. Process for improving the fire-retardant properties of lignocellulosic products which comprises chlorinating or brominating said products to a chlorine or bromine content of from 2 to 12 weight percent and thereafter reacting the chlorinated or brominated products with a trialkyl or triaryl phosphite or phosphonate at a temperature of from 100 to 150 C.

2. Process of claim. 1 wherein the lignocellulosic products are wood.

3. Process of claim 2 wherein the phosphorus com pound is a trialkyl phosphite or phosphonate wherein the alkyl group contains from 1 to 4 carbon atoms.

UNITED STATES PATENTS 1,936,985 11/1933 Lommel et al.

2,574,515 11/1951 Walter et al. ll7-136 X 3,092,537 6/1963 Brandts 117-136 X 3,150,919 9/1964 Lewin 117136 X 3,288,890 11/1966 Blake et al 117137 X 3,321,330 5/1967 Mohney 117-136 WILLIAM D. MARTIN, Primary Examiner H. S. GWINELL, Assistant Examiner US. Cl. X.R. 

